Just trying to educate myself. I have somewhat of an understanding about cam lift numbers and what they mean..however... what about duration numbers? How does say a 230/236 - 112 differ from something like MTI's X1 cam that is 230/227 - 112. Is this specific to say an NA motor vs. n20/boost?? Pros vs. cons?? Teach me something Thanks

Aaron

 

Well for starters if I had to guess I would say the first was a gen 1 or LT1 cam and the second an LSx cam.
Reason I say that is gen 1 and 2 heads almost always need some help on the exhaust because it is weak compared to the intake flow so higher exhaust duration is used as a bandaid. With the LSx motors there are cams available with more intake duration than exhaust, I have no experiance with the LSX motors so I can only assume they have a better intake to exhaust flow ratio than the gen 1-2 motors and that is why cams are offered like that.

Have I run into you at WIR?

 

Take a look at the catalog of a large cam company (Crane, Comp, etc.) and see how the numbers for different engine families and within families for cams of different uses. Typically, rpm range, needed CR, typical use, etc. will be listed. You can learn a lot about the chracteristics of cams from a study of this information, lacking in detail though it may be. As you start to develop a feel, look in more detail at the cam card information paying attention to the valve events.

To get an idea of how valve events relate to performace characteristics, take a look at the sticky I wrote in the N2O Techsection about nitrous cams. That specific example concerns the importance of the exhaust valve opening. BTW, in general terms the intake valve closing point (IVC) is the single most important valve event. To get a feel for that, search this site for "dynamic compression" and "DCR". Keep in mind that most people who post in these threads are just parroting what a few others have posted, don't take anything for gospel. You might want to look at a tech page I wrote about DCR, which you can see here: http://www.kennedysdynotune.com/Dyna...ion%20Tech.htm

Rich

 

Thanks for the info guys, yes Dwayne I've ran into you at WIR before. I use to run down there a bit, however I sold my camaro a little over a year ago as I simply didn't have time to drive it. I was away from home a lot with a new job and needed the $$ more than the car. Thanks again.

Aaron

 

Jesus Dwayne.... that's not even close.

REVERSE SPLIT CAMS DON'T WORK BETTER!!!!!

If you have a motor with long runners that works on a lower harmonic wave (lower number of harmonics the higher the amplitude of the wave) then it will fill the cylinder better most likely and you will need to get MORE exhaust out of the motor, since the CYLINDER IS FILLED BETTER!

Even on 2bbl race motors you don't want a reverse split cam, and that's a situation where there is weak wave tuning and a very high vacuum in the intake track, which means crappy cylinder filling.

So if a long runner, high flowing, large throttle body motor (ie LS1) doesn't like a reverse split and a short runner, dual plane, small carb motor (2bbl race) doesn't like a reverse split... WTF DOES?

NOTHING.

Notice I mentioned nothing about a E/I% flow ratio.... because the steady state FLOW you get on a bench doesn't = cylinder filling.

Bret